Multiphase magnetic overprints in the Moine Thrust Zone

Abstract

AbstractPalaeomagnetic studies from the southern part of the Moine Thrust Zone (MTZ) indicate a complex pattern of four major secondary remanence components (A–D). Their relative ages appear to vary from mid-Ordovician to Recent/Tertiary. The oldest remanence (A) is tentatively interpreted as associated with the formation of the Lochalsh Syncline (D1) and/or D2. However, the consistency between component A and the regional southeast-plunging lineation, makes it uncertain to what extent component A reflects the structural grain rather than a true palaeofield record. Component B appears to be associated with early Devonian uplift along the MTZ relating to localized shearing/high level brittle thrusting, and is almost synchronous with the emplacement of lamprophyre and felsic dykes.In the inverted limb of the Lochalsh Syncline, and beneath the Balmacara Thrust, possible Permian (component C) and Recent/Tertiary magnetic overprints are recognized. Component C is partly of high magnetic stability and may indicate localized shears in the inverted limb, usually considered as Caledonian shearing. It is uncertain to what extent the youngest component (D), essentially recorded in rocks close to the Balmacara Thrust in mylonites and fault breccias, reflects important tectonic reactivation and magnetic resetting. This component is governed by low stability magnetic phases with blocking temperatures below 200 °C.